• Objects
• Arrays
• Strings
• Hashes
• Classes

Everything in Ruby is an object

        1.is_a?(Object)       # true
        Array.is_a?(Object)   # true
        Object.is_a?(Object)  # true
      

Specialized functions for various types of data

Used to store a list of things

        a = Array.new         # []
        a.push(1)             # [1]
        a.unshift('a')        # ['a',1]
        a.insert(1, "index")  # ['a', 'index', 1]
      

Useful when the order is important (queue)

        a = [1,2,3,4]
        a.length  # 4
        a.pop     # 1
        a.length  # 3
        a.pop     # 2
        ...
      

Can be treated as a set

        a = [9,3,4,1,2,3,4]
        a.uniq!   # [9,3,4,1,2]
        a.sort!   # [1,2,3,4,9]
      

Used to store characters

        a = "hello"   # "hello"
        a += " "      # "hello "
        a << "world"  # "hello world"
        a.concat(33)  # "hello world!"
      

They are really an array of characters

        a = "abcd"
        a[0..2]   # "abc"
      

Nice functions to format text

        a = "Aloha"
        a.downcase    # "aloha"
        a.upcase      # "ALOHA"
        a.capitalize  # "Aloha"
      

Used as a key / value store

        a = Hash.new    # {}
        a[1] = "one"    # { 1 => "one" }
        a["two"] = 2    # { 1 => "one", "two" => 2 }

        a.keys          # [1, "two"]
        a.values        # ["one", 2]
      

Useful when you want to perform a lookup

        lookup = { "matt": "647-123-4444" }
        lookup[:matt]   # "647-123-4444"

        lookup.fetch(:ben, "No number found")
      

A way of making your own objects

Grouping functions by purpose / category

        class ClearFit
          def self.pitch
            "Find the right jobs for people"
          end
        end

        ClearFit.pitch